Beta-alumina-based sintered compact and its production method

Abstract

To provide a dense beta-alumina-based sintered compact having a high ionic conductivity as a solid electrolyte by firing at a low temperature to suppress the volatilization of Na 2 O and its production method. By adding RNbO 3 which is a material having a low melting point to a beta-alumina powder, followed by firing, it is possible to obtain a beta-alumina-based sintered compact having a low firing temperature and containing, as the main component, dense β″ alumina crystals which are free from anomalous grain growth during the firing process.

What is claimed is: 
     
       1. A beta-alumina-based sintered compact, comprising:
 a beta-alumina crystalline phase having Na 2 O and Al 2 O 3  as main components; and 
 an RNbO 3  crystalline phase; 
 wherein R is at least one element selected from the group consisting of Li, Na, and K. 
 
     
     
       2. The beta-alumina-based sintered compact according to  claim 1 , wherein the beta-alumina crystalline phase comprises a β″ alumina crystalline phase. 
     
     
       3. The beta-alumina-based sintered compact according to  claim 1 , wherein R is Na. 
     
     
       4. The beta-alumina-based sintered compact according to  claim 1 , comprising NiO as a component. 
     
     
       5. The beta-alumina-based sintered compact according to  claim 4 , wherein a chemical composition of the beta-alumina-based sintered compact, based on oxides, is:
 from 8 to 15 mass % of Na 2 O; 
 from 5 to 30 mass % of Nb 2 O 5 ; 
 from 1 to 10 mass % of NiO; and 
 a remainder of Al 2 O 3 . 
 
     
     
       6. A method for producing the beta-alumina-based sintered compact as defined in  claim 1 , comprising:
 mixing a beta-alumina powder and an RNbO 3  powder; and 
 molding and firing the mixture; 
 wherein R is at least one element selected from the group consisting of Li, Na, and K. 
 
     
     
       7. The method for producing the beta-alumina-based sintered compact according to  claim 6 , wherein firing the mixture comprises firing at a temperature of less than 1450° C. 
     
     
       8. The method for producing the beta-alumina-based sintered compact according to  claim 6 , wherein the beta-alumina powder comprises β″ alumina. 
     
     
       9. The method for producing the beta-alumina-based sintered compact according to  claim 6 , wherein R is Na. 
     
     
       10. The method for producing the beta-alumina-based sintered compact according to  claim 6 , wherein the beta-alumina powder comprises NiO. 
     
     
       11. The method for producing the beta-alumina-based sintered compact according to  claim 10 , wherein a chemical composition of the beta-alumina-based sintered compact, based on oxides, is
 from 8 to 15 mass % of Na 2 O; 
 from 5 to 30 mass % of Nb 2 O 5 ; 
 from 1 to 10 mass % of NiO; and 
 a remainder of Al 2 O 3 . 
 
     
     
       12. A beta-alumina-based sintered compact, comprising:
 as chemical components, based on oxides, Na 2 O and Al 2 O 3 ; and 
 as a crystalline phase, a beta alumina crystalline phase and an RNbO 3  crystalline phase; 
 wherein R is at least one element selected from the group consisting of Li, Na, and K. 
 
     
     
       13. The beta-alumina-based sintered compact according to  claim 12 , wherein the beta-alumina crystalline phase comprises a β″ alumina crystalline phase. 
     
     
       14. The beta-alumina-based sintered compact according to  claim 12 , wherein R is Na. 
     
     
       15. The beta-alumina-based sintered compact according to  claim 12 , comprising NiO. 
     
     
       16. The beta-alumina-based sintered compact according to  claim 15 , wherein a chemical composition of the beta-alumina-based sintered compact, based on oxides, is:
 from 8 to 15 mass % of Na 2 O, 
 from 5 to 30 mass % of Nb 2 O 5 ; 
 from 1 to 10 mass % of NiO; and 
 a remainder of Al 2 O 3 .